I think they should do exactly what they want to do in their own marriage. With her cancer and subsequent surgeries I can understand why they wouldn't want to get married in the middle of all of that and I think it probably made the ceremony and committment all that more special.
Angelina Jolie and Brad Pitt have shown the world that love makes a family. They have supported their children for years and years and have done a wonderful job at that. It is their personal decision when they get married and they've chosen to wait. 50% of American marriages end in devorce - there is something to be said about waiting and making sure that the person you marry is the person you want to spend the rest of your life with.
I feel like this is a subjective topic. The only people that really know how their marital bliss is going is Angelina Jolie and Brad Pitt. The rest of us are merely speculating on whether or not these two people are happy with their marriage. I feel that ultimately they made a decision that was right for them, and that is a good thing.
No I do not think that Brad Pitt and Angelina Jolie should have gotten married much sooner. They got married when they wanted to and when they felt was the right time. Only they know when the right time was to make sure that the marriage is going to work.